1. Field of the Invention
The invention relates to a method of synthesis of metal nanoparticles and fibers, such as Cu, Pd, Pt, Ag and Au nanoparticles and Cu sub-micron fibers, by using carbon nanotubes or carbon nanofibers as templates.
2. Description of the Related Art
Metal nanoparticles are widely used in catalysis, electrical and optical devices and coatings etc. For example, Pt, Pd, Au, and Ag nanoparticles are excellent catalysts for hydrogenation of unsaturated hydrocarbons, complete oxidization of NO or CO, and dehydrogenation of alcohol etc. Au, Ag, and Cu thin films can be used as IR-deflection films in certain devices and show optical performance superior to other materials.
The following part of this section is a summary of the current methods known for the preparation of metal nanoparticles [1]:
1. Metal Evaporation at Low Pressure
In this method, bulk metal is evaporated in an Ar or He atmosphere under low pressure. The productivity, size and size distribution of the particles formed are all controlled by the way the metal is heated. Normally, metal particles with diameters ranging from 1 to 1000 nm can be obtained. However, this method is only suitable for low melting point materials.
2. Hydrogen Plasma-assisted Metal-melting
In this method, metal is melted by an arc generated between a hydrogen plasma and a metal. Ar, N2 and/or H2 dissolve in the molten metal, then release from the melt and transport ultra-fine metal particles.
3. Nanoparticles from Supersaturated Vapor
The supersaturated vapor method is the earliest method known for preparing nanoparticles. The process includes three steps: 1) production of a supersaturated vapor; 2) nucleation, growth and agglomeration of particles; and 3) collection of the particles. The most important step of this method is the generation of the supersaturated vapor. Until now, thermal evaporation, sputtering, electron beam evaporation, laser ablation, etc., have been applied in supersaturated vapor generation.
4. Metal Evaporation on the Surface of a Fluid
In this method, metal is evaporated under a high vacuum, then quenched in a specified fluid. Nanoparticles with controllable diameters can be obtained via this method. In addition, the size distribution of the particles is relatively narrow.
Recently, S. Ayyappan et al. reported that nanoparticles of Ag, Au, Pd and Cu could be obtained by the reduction of corresponding metal salts using ethyl alcohol as the reducing agent under refluxing conditions[2]. In order to control the formation of the metal colloids and to stabilize them, polyvinylpyrrolidone (PVP) was employed as a protective agent. However, considerable particle agglomeration was unavoidable. Such a problem was also encountered by Z. Paszti et al[3] in the production of Cu and Ag nanoparticles by using a laser ablation method.
The discovery of carbon nanotubes has generated great research activity worldwide. The morphology and tubular structure of this material enables it to function as a specific template in synthesizing nano-rods and nanoparticles. In most cases, the nano-rods and nanoparticles are formed inside the tube[4] or the tubes need acid pre-treatment[5]. According to embodiments of the present invention, some commonly used metal nanoparticles, such as Pd, Pt, Cu, Ag and Au were successfully prepared with diameters ranging from less than 5 to tens of nanometers, as were Cu sub-micron fibers, by using carbon nanotubes or nanofibers as templates.
The present invention is directed to a process for advantageously synthesizing metal nanoparticles and sub-micron fibers.
The method for forming metal particles and fibers, includes: mixing at least one of nanotubes and nanofibers with at least one metal salt to form a mixture; and decomposing the mixture.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.